Police arriving at Wednesday's crime scene reportedly ordered witnesses to delete photos of the head which they took with their phones.

"It seemed as if the head was placed in a way that made it look like it was staring through the front window of the lounge, as some sort of warning," a witness told Dutch daily Het Parool.

The shisha bar is said to be a gathering spot for criminals involved in the so-called "Mocro-war", a power struggle mainly between Dutch-Moroccan gangs in the city.

The severed head most likely represented a "new phase" in the gang war, which has seen several others murdered in Amsterdam, including one man who was killed after visiting the same bar, Dutch media reports said..